Russia’s new nuclear weapons are technically plausible…

ON MARCH 1st, addressing Russia’s parliament, President Vladimir Putin announced a range of new, high-tech, “invincible” nuclear weapons. Lest anyone was unsure at whom that part of the speech was aimed, it featured a computer-generated animation of nukes falling on Florida, where Donald Trump, America’s president, has his Mar-a-Lago resort.

Mr Putin’s new weapons included nuclear-powered, nuclear-tipped cruise missiles with nearly infinite range and nuclear-armed underwater drones designed to creep up on enemy ports before destroying them. Though they sound fantastical, most of the new weapons are technically feasible. Underwater drones, for instance, already exist. Bolting a nuclear warhead to one poses no fundamental difficulties. The real question is whether there is any strategic or tactical need for them.

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Most of the headlines focused on a cruise missile that sports a nuclear engine as well as a nuclear warhead. The idea is not new. The American Supersonic Low Altitude Missile (SLAM) project explored such a scheme in the 1950s and 1960s. A cruise missile was to be powered by a nuclear reactor, which would heat air to produce thrust. The missile would have been able to fly several times around the world, and to carry many nuclear bombs at once. The engine worked in ground tests, although its radioactive exhaust (and the risk of mishap) meant it was deemed impossible to conduct trials in the air. The SLAM was abandoned as scientists perfected intercontinental ballistic missiles (ICBMs). But according to both Mr Putin and unnamed American officials, the Russian missile has already made test flights.

A new ICBM was the most familiar bit of Mr Putin’s speech. Russia has been working on the RS-28 missile for years, as a replacement for its existing systems. He said it would be powerful enough to deliver its warheads via the South Pole, dodging American missile-tracking radars which cover the shorter route over the Arctic.

Russian warheads are to be pepped up, too, to be capable of gliding and evasive manoeuvres even at the hypersonic speeds at which they travel, and possibly lofted by yet another new ICBM. This too is an old idea, dating back to the 1930s. Technological developments have now made it practical. America conducted at least four tests of a non-nuclear version of such a weapon between 2010 and 2014; China has also run tests, though how it would arm its system is unclear.

So the whizzy new weapons are probably workable, at least in principle. A bigger question is whether there is any reason to build them. Mr Putin said the weapons were a response to America’s withdrawal in 2002 from the Anti-Ballistic Missile Treaty, which limited the development of defences that could shoot down ballistic missiles. Since then, America has deployed limited versions of these defences in eastern Europe and Asia, as well as in America itself, and at sea. Highly manoeuvrable warheads, missiles that can be fired over the South Pole, supersonic cruise missiles and underwater port-busters are all threats that such defences can at present do nothing against.

America insists its defences are meant only to guard against “nuclear blackmail” by states such as North Korea or Iran, not to upset the equilibrium of mutually assured destruction that, in theory, acts as a final safeguard against nuclear war. Russian military planners might be reluctant to trust such assurances. But Russia’s existing arsenal of hundreds of missiles and thousands of warheads could easily overwhelm any defence through sheer weight of numbers. There is no practical need for exotic new weapons. But Mr Putin may have a political, or even a personal, one.